Recent developments in breakerless ignition system technology have made available highly efficient and reliable capacitive discharge ignition systems for internal combustion engines of all sizes. Initially, breakerless ignition systems were designed and used primarily for larger horsepower engines, but as electronic ignition systems of this type became more prevelant, the use of such systems in small horsepower internal combustion engines became highly feasible. Not only have breakerless ignition systems been recently installed in new low horsepower internal combustion engines, but the efficiency and reliability of these systems have led to an ever-increasing demand for retrofit units which can replace the breaker point ignitions presently installed in the tremendous number of low horsepower internal combustion engines presently in existence in the field.
When designing a breakerless ignition system to be retrofit on an existing engine, a number of unique problems and requirements must be met which do not normally arise with ignition systems which are installed in a new engine designed to receive the ignition system. For example, with retrofit units, it is often highly desirable that the unit to be attached to the engine does not either increase the engine profile or interfere with engine components which are already in place. This means that external components of the ignition system to be retrofit must be designed to operate effectively while accommodating existing engine components and maintaining the existing engine profile.
In previous breakerless ignition systems designed to be retrofit on existing engines, a particularly perplexing problem was presented by the ignition system control box which contains the highly inductive spark producing transformers for the breakerless ignition system plus associated control board circuitry. Due to the nature of these highly inductive transformers and the circuitry associated therewith, ignition control boxes are normally formed of heavy cast metal and must be both strong and water tight to protect the internal circuitry against the effects of moisture. In a retrofit system, the ignition control box is normally secured externally to an internal combustion engine, and the inherent bulky configuration of this box makes it extremely difficult to maintain the engine profile. When the box is reduced in size, the difficulty of providing effective shielding to isolate the ignition transformers within the box is increased, but of even greater importance is the fact that on many engines, the ideal location for such a box is in the exact location of an engine air inlet hose which extends from the engine air filter to the intake manifold. If the ignition control box is connected to the engine beneath this air inlet hose, the hose is forced outwardly beyond the engine profile and is exposed to impact damage from articles moving in the vicinity of the engine. In the past, this exposure of the engine air inlet hose with the attendant increase in the overall engine profile has proven unacceptable, and in an attempt to alleviate this problem, a cutaway portion was formed in the outer cover of the ignition control box and in the box body so that the hose may be freely received in the resulting indentation. Although this design permits the engine air inlet hose to be maintained within the confines of the existing engine profile, the structure was found to be subject to a number of disadvantages, some of which contributed to the malfunction of the ignition system in the engine. First, the formation of an indentation extending inwardly from the front or cover section of the ignition control box into the box body seriously weakened the overall box structure. A more important structural deficiency, however, was the fact that the mating edges of the box and the box cover were forced to follow the profile of this identation, and effective moistureproof gasketing along this irregular line proved to be impossible. Consequently, moisture was admitted to the circuitry and the transformers within the ignition control box.
Another disadvantage experienced with the previous control box having the engine air inlet hose receiving indentation in the cover thereof was the fact that the cover of the box could not be removed without first disconnecting the air inlet hose from the engine. Finally, the air inlet hose merely rested in an indentation in the box and was not positively retained by the box to preclude damage to the hose.